At about 327,000 miles (527,000 kilometers) from Saturn, Rhea orbits inside the planet's magnetic field. Rhea's oxygen atmosphere is believed to be maintained by the ongoing chemical breakdown of water ice on the moon's surface, driven by radiation from Saturn's magnetosphere.
The Hubble Space Telescope and NASA's Galileo probe found in 1995 that a similar process creates tenuous oxygen atmospheres on Jupiter's ice moons Europa and Ganymede.
"The major implication of this finding at Rhea is that oxygen atmospheres at icy moons, until now only detected at Europa and Ganymede, may in fact be commonplace around those irradiated icy moons throughout the universe with sufficient mass to hold an atmosphere," said study leader Ben Teolis of the Southwest Research Institute in San Antonio, Texas.
Knowing where and how oxygen exists in the universe may in turn help scientists plan future robotic and manned missions.
But don't go investing in any Hoth inspired resorts to be built on Rhea just yet...
While the presence of oxygen does imply that a human colony cold theoretically thrive on Rhea, there is little chance that there will ever be a human colony on the icy satellite...
For one thing, the 932-mile-wide (1,500-kilometer-wide), ice-covered moon is more than 932 million miles (1.5 billion kilometers) from Earth. For another, the average surface temperature is -292 degrees Fahrenheit (-180 degrees Celsius).
And at less than 62 miles (100 kilometers) thick, the newfound oxygen layer is so thin that, at Earthlike temperatures and pressure, Rhea's entire atmosphere would fit in a single midsize building.
Still, the discovery implies that worlds with oxygen-filled air may not be so unusual in the cosmos puts a fresh puff of wind in the sails of the increasingly popular "Space Colony Movement".
While Rhea is unfavorable for a human colony, it doesn't necessarily mean that somebody else does not already call the icy world "Home".
NASA's Cassini spacecraft, which has been orbiting the Saturnian system since 2004, detected the oxygen atmosphere around Rhea during a close flyby of the icy moon in March.
Cassini's data show that molecular oxygen (O2) forms inside the moon's surface ice when water molecules (H2O) are split by energetic ions, a process known as radiolysis. The oxygen then gets ejected from the surface ice and captured by Rhea's gravity to form the atmosphere. Cassini also identified the distinctive chemical fingerprint of carbon dioxide in Rhea's atmosphere, indicating the presence of carbon on the moon's surface.
The combination of carbon and oxygen holds implications for finding possible life on ice moons, such as Europa, thought to harbor subsurface liquid oceans.
"You would expect a very small amount of gas [around an ice moon], but the fact that there is enough to be measurable is what is surprising and indicates that the energetic processes that must be occurring are more widespread than previously thought," said Robert Carlson, a researcher at NASA's Jet Propulsion Laboratory in Pasadena, California.
"Specifically this indicates that the surface is oxidizing, meaning that you can make alcohols and organic acids if carbon is in the surface materials," said Carlson, who wasn't involved in the study.
"There are also ideas that the oxidants, like O2, could be subducting into an ocean below the surface and could be an energy source for any life in these possible oceans."
To Boldly Go...
As the topic of extraterrestrial human colonies begins to grow in popularity- both among the plebs and the powerful- the beginnings of understanding the chemistry of the universe have astronomers giving a new look to something known in science fiction for years...
It’s all about the moons...
From Pandora to Endor, life is always readily discovered on the fictional moons orbiting the large gas giants in sci-fi films and text.
Maybe it could be like that in real life too...
"The discovery of Rhea's atmosphere is extremely fortuitous, as it will allow us to anticipate what we might expect to find at Jupiter's moons and design the spacecraft instruments accordingly," study leader Teolis said.
[Jupiter's moon, an orb known as Europa- is thought by many astronomers to be the best shot in our universe to discover extraterrestrial life (anything from aquatic vegetation to more complex organisms).]
This is also great news for the future of man's adventures into deep space exploration as a whole.
"This shows how prevalent high-energy chemistry is on icy satellites, not constrained to just Europa," Carlson said.
Knowing that water, oxygen, and carbon dioxide- necessary to sustain life in all Earth bound plants and animals (including us humans)- can be found on the frozen moons of the gas giants may one day be pivotal for deep-space exploration involving human missions.
"In some very distant—and highly speculative—future," he said, "one can imagine that the ices on these moons might be heated or melted to extract oxygen and carbon dioxide, both of which are necessities for the survival of plant and animal life."
Human colonies in oxygen rich planets, mining icy worlds for water and air... these are all concepts deeply woven into the fabric of modern science fiction...
All coming to fruition in the realm of the real.Let’s just hope that's all sci-fi got right about outer space...